In three-dimensional printing, building material is selectively jetted from one or more printing heads and deposited onto a fabrication tray in consecutive layers according to a pre-determined image data. In printing machines that utilize photopolymers as building material, the liquid layers are solidified, conditioned or cured using a radiation source. The radiation source may emit light such as ultraviolet (UV) light according to predetermined working parameters, such as output radiation intensity and spectral region. Formation of high-quality 3D objects requires maintaining the radiation power and wavelength region substantially constant. For example, the radiation power may only vary within ±5%-±10%. The intensity of the light source, however, may decrease in more that 10% from various reasons including deterioration of the light source, deterioration of a reflector of the light source, appearance of mist or undesired splashes of material on the protective glass of and the like. Further, the desired spectral region of the light source may shift so that light may be at less effective wavelengths. Accordingly, there is a need to monitor the radiation power and other characteristics of the radiation source.
It will he appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the drawings to indicate corresponding or analogous elements. Moreover, some of the blocks depicted in the drawings may be combined into a single function.